In the braking operation of a moving vehicle, the mechanical system of the tooth wheel and sensor can go into oscillations with the result that noise and spurious signals are generated. These unwanted interfering signal frequencies can lead to faulty operation of the anti-skid vehicle brake system.
A previously preposed switching circuit is based upon the premise that the amplitudes of the spurious signals are as a rule considerably smaller than the amplitudes of the useful signal. In such a switching circuit, it is generally assumed that there is a certain amplitude ratio between the information bearing signals and the interfering spurious signals. Under such an assumption, it is common practice to suppress the interfering signals or spurious noise frequencies with the aid of threshold stages. It has been found, however, that in the case of axial generators and rotary oscillation devices, there frequently appears spurious noise signals with amplitudes on the order of magnitude of the amplitudes of the useful signals.